## Quantum Simulation of Rainbow Gravity

Rainbow gravity modifies general relativity by introducing an energy dependent metric, which is expected to have a role in the quantum theory of black holes and in quantum gravity at Planck energy scale. We show that rainbow gravity can be simulated in the laboratory by nonlinear waves in nonlocal media, as those occurring in Bose-condensed gases and nonlinear optics. We reveal that at a classical level, a nonlocal nonlinear Schr\”odinger equation may emulate the curved space time in proximity of a rotating black hole as dictated by the rainbow gravity scenario. We also demonstrate that a fully quantized analysis is possible. By the positive $\mathcal{P}$-representation, we study superradiance and show that the instability of a black-hole and the existence of an event horizon are inhibited by an energy dependent metric. Our results open the way to a number of fascinating experimental tests of quantum gravity theories and quantum field theory in curved manifolds, and also demonstrate that these theories may be novel tools for open problems in nonlinear quantum physics.

The picture below shows spectra and configuration of particles trapped in a quantum simulation of a black-hole.

Braidotti and Conti, in ArXiv:1708.02623

## Glauber oscillator and time travel

The standard quantum mechanics does not forbid time-travel. However, some alternative formulations (based on the so called “rigged Hilbert space”) include irreversibility as a fundamental principle: a quantum particle that decays cannot travel back in time.

There are not direct evidences of the irreversibility of decay processes, but the new quantum mechanics predicts that the decay rates are quantized.

If one observes the quantization of the decay rates, one can claim to have provided experimental support to the irreversible formulation of quantum mechanics.

In simple terms, one can claim that time-travel is not possible at the quantum level (…and also at the classical level).

Silvia Gentilini, Maria Chiara Braidotti, Giulia Marcucci, Eugenio Del Re, and Claudio Conti simulated in the laboratory one of the simplest models of the irreversible quantum mechanics, that follows an original proposal of Glauber. A laser beam emulates a quantum particle in a reversed harmonic oscillator, as a result the first experimental evidence of the quantization of decay time is reported in a paper published in Scientific Reports.

(reprint from the former complexlight.org website)

## Solitons and quantum gravity in the Hawking radiation

The fact that solitons may have a role in quantum gravity is intriguing.

In a paper in ArXiv, by Leone Di Mauro Villari, Giulia Marcucci, Maria Chiara Braidotti (all of them top complexlight students), and CC, a toy model concerning Hawking radiation by moving black holes is proposed.

Within a simple one-dimensional theory, based on solitons of the Sine-Gordon equation, the authors claim that Hawking emission may be extracted by the concomitant observation of gravitational and electromagnetic waves emitted by colliding black holes. The effect is due to the black-hole-velocity dependent emission spectrum (figure above), which results into an electromagnetic frequency chirp detected by the observer.

## Black holes evaporate, black holes are solitons, solitons evaporate !

The fact that black holes are solitons is not very well known. Abdus Salam and others outlined this issue several years ago. Stephen Hawking predicted that Black Holes evaporate, and this is a quantum effect on classical gravity governed by the highly nonlinear Einstein-Hilbert equations.

Leone Villari, Ewan Wright, Fabio Biancalana and Claudio Conti report on the possibility that all types of classical solitons may evaporate in the quantum regime. A paper in the arXiv contains the theory on the exact quantization of the nonlinear Schroedinger equation: solitons emit a blackbody radiation spectrum at a temperature given by the same formula of Hawking!

This result is intriguing. On one hand, because it represents the first theoretical prediction of the Hawking radiation in a fully nonlinear quantum field theory. The standard Hawking theory relies on the quantization of a linear field in a curved background. The theory may hence provide insights for a true quantum gravity based on the complete quantization of the Einstein-Hilbert equations.

On the other hand, the result is also important because the Hawking radiation from a quantum soliton may furnish a novel highly tunable quantum source with many possible applications.

## Generalized Uncertainty Principle and the Photon (Templeton project)

In recent years, researchers question about the limits of the uncertainty relation.

Hints from quantum gravity theories suggest that the Heisenberg principle should be generalized.

Some considered implications in high energy physics, others have considered the mechanical motion of massive objects to look for possible tests of these supposed limits to the most important paradigm of quantum mechanics.

In a project funded by the John Templeton Foundation (grant number 58277), we consider the case of the photon, and study the possible way a generalized uncertainty principle may play a role in modern photonics, nonlinear and quantum optics.

The project started in 2015 and will finish in 2018, stay tuned.

Related posts:

The Quest for Quantum Gravity in Optics

The Math of Irreversibility

Black holes evaporate, black holes are solitons, solitons evaporate !

Time Travel is NOT Possible (press release)